Cold and flu season is upon us, and before your office turns into a chorus of coughs and sneezes, consider protecting yourself by stocking up on immune-boosting, nutrient-dense "superfoods" that will help improve your body's ability to fight off disease.

"Nutrient-density refers to the amount of essential nutrients or health-promoting phytochemicals provided per calorie," says Tonia Reinhard, senior lecturer in nutrition and food science at Wayne State University in Detroit and author of Superfoods: The Healthiest Foods on the Planet (Firefly Books, 2010). She recommends these five superfoods during cold and flu season:

1. Salmon. Fatty fish such as salmon, is high in protein and omega-3 fatty acids. "Protein is needed to synthesize the structures of the immune system [including] skin, membranes and cells and antibodies," says Reinhard. Without these structures, the immune system is like a soldier without a sword and is left defenceless against viruses and bacteria invaders. Reinhard recommends two or more 3-ounce servings a week.

2. Greek yogurt. This high protein yogurt is also chocked full of probiotics. "Yogurt that contains live cultures promotes a strong immune system because the friendly bacteria in yogurt keeps the [bad] bacteria from increasing in number," says Reinhard. Reinhard recommends an 8-ounce serving per day.

3. Eggs. One medium-sized egg contains 6.8 grams of protein (The FDA recommended daily amount of protein is 50 grams). Protein is essential to building muscle and keeping your body strong. Eggs are also rich in vitamins and minerals, including B6 and B12 which contribute to a healthy immune system.

4. Nuts. A high protein snack, nuts are also an excellent source of selenium and zinc – two minerals that are essential for immune system health. Brazil nuts have one of the highest selenium contents and Japanese chestnuts have high zinc content.

5. Bell peppers and dark leafy greens. Although you may think of citrus when it comes to getting more vitamin C, bell peppers and dark leafy greens such as kale, spinach, romaine lettuce, brussels sprouts and broccoli pack a better punch. While Reinhard says vitamin C can't make a cold or flu go away, it can reduce the time you're affected by it.

Red bell peppers have almost three times the vitamin C content as an orange. Reinhard recommends eating at least some of these vegetables raw, or dipped in hummus for some extra protein, to maximize nutritional content. "Vitamin C is high in many vegetables, but [cooking them] reduces vitamin C content," she says.